1. Field of the Invention
The present invention relates to the technical field of imaging optical systems and imaging apparatuses, specifically to the technical field in which a light control element that adjusts the quantity of incident light for an image sensing device, and an optical filter that includes an infrared absorbing material are used to ensure a desirable white balance regardless of the density of the light control element, and to realize desirable color reproducibility concerning the red region.
2. Description of the Related Art
There have been recent demands for miniaturization of imaging apparatuses, such as digital video cameras and digital still cameras, with maintained high resolution.
To meet such demands, imaging apparatuses have been proposed that include a miniaturized imaging optical system, and a high-density CCD (Charge Coupled Device) or a high-density CMOS (Complementary Metal-Oxide Semiconductor) installed as an image sensing device.
However, miniaturizing the imaging optical system reduces the aperture area of the aperture stop, and thus produces considerable image deterioration due to a diffraction phenomenon.
In some imaging apparatuses, the light quantity control mechanism that adjusts the quantity of incident light for the image sensing device is realized by, for example, a mechanical iris system that mechanically drives the aperture blades or ND (Neutral Density) filter using an actuator. This type of imaging apparatus using a mechanical iris system requires a large space for disposing the iris system, and cannot be miniaturized to sufficient levels.
As a countermeasure, other type of imaging apparatus adjusts the quantity of incident light for the image sensing device with an electrical iris system, using a light control element of electrochemical material such as liquid crystal or EC (electrochromic) material (see, for example, JP-A-7-20529, JP-A-11-326894, and Japanese Patent No. 3918500).